1. Field of the Invention
The present invention relates to a data processing apparatus for processing data each time the data is supplied.
2. Description of the Related Art
There is a data processing apparatus for processing data in accordance with a predetermined program when the data is supplied. As a conventional apparatus of such a data processing apparatus, as shown in FIG. 1, a data existence position display pulse is supplied to a differentiating circuit 1. The data existence position display pulse is a signal which is supplied as another signal different from a data signal and which is supplied so as to form a pair together with the data signal or is a signal locating at the head of the data signal as a part thereof. When the data existence position display pulse is supplied to the differentiating circuit 1 as shown in FIG. 2(a), the differentiating circuit 1 differentiates the data and generates a trigger signal as shown in FIG. 2(b). A data processing circuit 2 is connected to an output terminal of the differentiating circuit 1. For instance, the data processing circuit 2 comprises a microcomputer. When the trigger signal is supplied, the data processing circuit 2 operates in response to a clock pulse and executes an arithmetic operation in accordance with the supplied data and generates data indicative of the result of the arithmetic operation as shown in FIG. 2(c).
However, in the conventional data processing apparatus, the differentiating circuit 1 must have a high response speed suitable to promptly respond to a leading edge of the data existence position display pulse when a pulse is supplied. Thus, there is a problem such that the differentiating circuit operates and generates the trigger signal not only in the case where the data existence position display pulse has been supplied but also in the case where a pulse-like noise signal has been mixed as shown by reference character A in FIG. 2(a), so that the data processing circuit 2 erroneously operates and generates data indicative of the wrong processing result. In addition, there is also a problem such that, since the output data, which is obtained until the operation of the data processing circuit itself according to the clock pulse is stabilized in the data processing circuit in response to the supply of the trigger signal cannot become the effective data, even in the case of the data which has been generated as shown in FIG. 2(c), the data of the portion other than the portion shown by reference character B in FIG. 2(d) is not the effective data.